Sixth International Conference on Dose, Time and Fractionation in Radiation Therapy "Biological and Physical Basis of IMRT & Tomotherapy" The University of Wisconsin (Department of Human Oncology) and the American Association of Physicists in Medicine (AAPM) will plan, organize and conduct a 3 day conference on "Biological and Physical Basis of IMRT & Tomotherapy." The Conference will provide a forum for discussion on the current status of the biological, physical/technological, and clinical aspects of time, dose, and fractionation schemes for radiation treatment of cancer patients and the several parametric models (both explanatory and predictive) of the volumetric effects thereof. There will be specific emphasis on the impact of emerging delivery methods of intensity modulated radiation therapy (IMRT) and Tomotherapy. The invited faculty and other participating speakers will present descriptions and assessments of the recent advances made in these delivery methods; in analytical models and techniques of modeling; in the concepts and methods of modern data analysis; in treatment optimization schemes; and in the elucidation of the basic mechanisms of radiation response. The progress to be reported is for the four-year period, 1998-2001, that has elapsed since the last such conference. The relevance of each of the above topics to clinical practice in Radiation Oncology will be emphasized. An evening workshop will provide tutorials in basic theory and methodology, as well as providing a forum for the identification and discussion of issues needing further investigation. At a concluding session, findings of the relevant current cooperative interdisciplinary studies will be presented and discussed. New studies will be developed to address some of the more insistent of the issues identified during the earlier discussions.